1. Field of the Invention
Embodiments of the invention relate to a stereoscopic image display.
2. Discussion of the Related Art
A stereoscopic image display implements a stereoscopic image, i.e., a three-dimensional (3D) image using a stereoscopic technique or an autostereoscopic technique. The stereoscopic technique, which uses a parallax image between user's left and right eyes with a high stereoscopic effect, may include a glasses type method and a non-glasses type method, both of which have been put to practical use. In the glasses type method, the parallax image between the left and right eyes is displayed on a direct-view display or a projector through a change in a polarization direction of the left and right parallax image or in a time-division manner, and thus a stereoscopic image is implemented using polarization glasses or liquid crystal shutter glasses. In the non-glasses type method, an optical plate such as a parallax barrier for separating an optical axis of the left and right parallax image is generally installed in front of a display screen.
The glasses type stereoscopic image display is classified into a polarizing glasses type stereoscopic image display and a shutter glasses type stereoscopic image display. In the polarizing glasses type stereoscopic image display, a polarization separation element such as a patterned retarder has to be attached to a display panel. The patterned retarder separates polarized light of left and right eye images displayed on the display panel. When a viewer watches a stereoscopic image through the polarizing glasses type stereoscopic image display using polarizing glasses, he or she sees polarized light of the left eye image through a left eye filter of the polarizing glasses and sees polarized light of the right eye image through a right eye filter of the polarizing glasses, thereby feeling a stereoscopic feeling.
In an existing polarizing glasses type stereoscopic image display, a liquid crystal display panel may be used as a display panel. In this instance, a parallax is generated between a pixel array of the liquid crystal display panel and a patterned retarder because of a thickness of an upper glass substrate of the liquid crystal display panel and a thickness of an upper polarizing plate. Hence, a narrow vertical viewing angle is obtained.
As shown in FIG. 1, a liquid crystal display panel 20 includes an upper glass substrate 4, on which a color filter 6 and black matrixes BM are formed, a lower glass substrate 2, on which a thin film transistor (TFT) array is formed, a liquid crystal layer (not shown) formed between the upper glass substrate 4 and the lower glass substrate 2, an upper polarizing plate 8 attached to the upper glass substrate 4, a lower polarizing plate 14 formed on the lower glass substrate 2, etc.
A patterned retarder substrate 12, on which a patterned retarder 10 is formed, is attached to the upper polarizing plate 8 of the liquid crystal display panel 20. The patterned retarder 10 includes first patterns 10a and second patterns 10b. The first patterns 10a are opposite to odd-numbered lines in a pixel array of the liquid crystal display panel 20, respectively, and the second patterns 10b are opposite to even-numbered lines in the pixel array of the liquid crystal display panel 20, respectively. Optical axes of the first pattern 10a and the second pattern 10b are different from each other. The first patterns 10a and the second patterns 10b retard a phase of incident light by about ¼ wavelength.
In the pixel array of the liquid crystal display panel 20, the odd-numbered lines may display a left eye image, and the even-numbered lines may display a right eye image. In this instance, light of the left eye image displayed on the odd-numbered lines of the pixel array is converted into linearly polarized light through the upper polarizing plate 8 and is incident on the first patterns 10a. Further, light of the right eye image displayed on the even-numbered lines of the pixel array is converted into linearly polarized light through the upper polarizing plate 8 and is incident on the second patterns 10b. The first patterns 10a retard a phase of the linearly polarized light incident through the upper polarizing plate 8 by about ¼ wavelength at a front viewing angle indicated by the dotted line shown in FIG. 1, thereby passing through left-circularly polarized light converted from the light of the left eye image. Further, the second patterns 10b retard a phase of the linearly polarized light incident through the upper polarizing plate 8 by about ¼ wavelength at the front viewing angle, thereby passing through right-circularly polarized light converted from the light of the right eye image. A left eye filter of polarizing glasses 30 passes through only the left-circularly polarized light, and a right eye filter of the polarizing glasses 30 passes through only the right-circularly polarized light. If the viewer wears the polarizing glasses 30, he or she sees only pixels of the odd-numbered lines of the pixel array on which, the left eye image is displayed, through his/her left eye and also sees only pixels of the even-numbered lines of the pixel array on which, the right eye image is displayed, through his/her right eye. Thus, the viewer can watch the stereoscopic image without 3D crosstalk at the front viewing angle.
The light of the left eye image displayed on the odd-numbered lines of the pixel array is converted into the linearly polarized light through the upper polarizing plate 8 at a vertical viewing angle indicated by the solid line shown in FIG. 1 and is incident on the first patterns 10a. In this instance, a portion of the linearly polarized light of the left eye image is incident on the second patterns 10b. Further, the light of the right eye image displayed on the even-numbered lines of the pixel array is converted into the linearly polarized light through the upper polarizing plate 8 at the vertical viewing angle and is incident on the second patterns 10b. In this instance, a portion of the linearly polarized light of the right eye image is incident on the first patterns 10a. Thus, the viewer wearing the polarizing glasses 30 sees pixels of the odd-numbered lines of the pixel array on which, the left eye image is displayed, and pixels of the even-numbered lines of the pixel array on which, the right eye image is displayed, through each of both eyes at the vertical viewing angle. As a result, when the viewer watches the stereoscopic image displayed on the polarizing glasses type stereoscopic image display at the vertical viewing angle, he/she watches a doubled image of the left eye image and the right eye image through his/her left or right eye, thereby feeling the 3D crosstalk.
To solve the 3D crosstalk at the vertical viewing angle in the polarizing glasses type stereoscopic image display, a method for forming black stripes BS on the patterned retarder as shown in FIG. 2 and a method for increasing a width of the black matrix BM of the liquid crystal display panel 20 as shown in FIG. 3 has been proposed. The black stripes BS additionally formed on the patterned retarder elongate in a line direction of the pixel array. As shown in FIG. 4, the black stripes BS overlap some of the odd-numbered lines of the pixel array and some of the even-numbered lines of the pixel array. A width of the black stripe BS is less than about ½ of a pixel pitch of the pixel array.
The method for additionally forming the black stripes BS on the patterned retarder as shown in FIG. 2 and the method for increasing the width of the black matrix BM as shown in FIG. 3 generate problems of a reduction in a light transmittance and a luminance. This is described below with reference to FIG. 5 and Equations (1) to (3).
In FIG. 5, ‘θ’ is a vertical viewing angle at which the 3D crosstalk may be generated; ‘P’ is the pixel pitch of the pixel array; ‘B’ is the width of the black matrix BM; ‘L’ is a distance (including a thickness of the glass substrate and a thickness of the polarizing plate) between a color filter array and the patterned retarder; and ‘n’ is an average refractive index of the glass substrate.
Equation (1) indicates geometric conditions inside a medium (i.e., the glass substrate and the polarizing plate). In Equation (1), ‘CTref’ is an allowable maximum value of the 3D crosstalk. Equation (2) indicates a relationship between an angle Φ of light traveling inside the medium by Snell's law and an angle θ of light emitted to the outside through the patterned retarder. Equation (3) is obtained through Equations (1) and (2).
                                          d            ·                          CT              ref                                +                      B            2                          =                  L          ⁢                                          ⁢          tan          ⁢                                          ⁢          ϕ                                    (        1        )                                          n          ⁢                                          ⁢          sin          ⁢                                          ⁢          ϕ                =                  sin          ⁢                                          ⁢          θ                                    (        2        )                                θ        =                              sin                          -              1                                ⁢                      {                          n              ⁢                                                          ⁢                              sin                (                                                      tan                                          -                      1                                                        (                                                                                                              (                                                      P                            -                            B                                                    )                                                ⁢                                                  CT                          ref                                                                    +                                              B                        2                                                              L                                    )                                )                                      }                                              (        3        )            
In the case of 47-inch FHD (full high definition) panel, P is 540 μm, B is 240 μm, L is 900, and n is 1.5 based on the 3D crosstalk of about 7%. When the above values are substituted for Equation (3), the vertical viewing angle satisfying the 3D crosstalk equal to or less than about 7% is estimated to be about 14.6° as shown in FIG. 18. The width B of the black matrix BM has to increase or the distance L between the color filter array and the patterned retarder has to decrease, so as to improve the vertical viewing angle. However, there is a limit to a reduction in the thickness of the glass substrate or the thickness of the polarizing plate. Therefore, because it is difficult to reduce the distance L, the vertical viewing angle may be improved by increasing the width B. However, when the width B of the black matrix BM increases, the transmittance of light in a 2D image and a 3D image is reduced. Hence, the luminance reduction is generated.